Interactions between the tonic and cyclic postural motor programs in the crayfish abdomen (original) (raw)
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The Journal of experimental zoology, 1993
Crayfish exhibit complex cyclical adjustments in abdominal posture during certain forms of backward walking. An isolated nerve cord preparation was used to investigate the properties of the interneurons which direct this alternation of abdominal flexion and extension. The command function for this cyclic postural behavior appears to be the domain of a distributed network of multiple pattern-initiating interneurons: each interneuron may be viewed as a command element within a command system. The cyclic pattern may be elicited by stimulation of small axon bundles pulled from the ventrolateral margins of any of the abdominal connectives. As few as one stimulus pulse to the axon bundle can elicit a single cycle of patterned output, although more pulses are generally necessary. This suggests some convergence or amplification step in the pattern-initiating interneurons. The amplification may be accomplished by several pattern-initiating interneurons that are coupled to one another and con...
Neural basis of a simple behavior: Abdominal positioning in crayfish
Microscopy Research and Technique, 2003
Crustaceans have been used extensively as models for studying the nervous system. Members of the Order Decapoda, particularly the larger species such as lobsters and crayfish, have large segmented abdomens that are positioned by tonic flexor and extensor muscles. Importantly, the innervation of these tonic muscles is known in some detail. Each abdominal segment in crayfish is innervated bilaterally by three sets of nerves. The anterior pair of nerves in each ganglion controls the swimmeret appendages and sensory supply. The middle pair of nerves innervates the tonic extensor muscles and the regional sensory supply. The superficial branch of the most posterior pair of nerves in each ganglion is exclusively motor and supplies the tonic flexor muscles of that segment. The extension and flexion motor nerves contain six motor neurons, each of which is different in axonal diameter and thus produces impulses of different amplitude. Motor programs controlling each muscle can be characterized by the identifiable motor neurons that are activated. Early work in this field discovered that specific central interneurons control the abdominal positioning motor neurons. These interneurons were first referred to as "command neurons" and later as "command elements." Stimulation of an appropriate command element causes a complex, widespread output involving dozens of motor neurons. The output can be patterned even though the stimulus to the command element is of constant interval. The command elements are identifiable cells. When a stimulus is repeated in a command element, from either the same individual or from different individuals, the output is substantially the same. This outcome depends upon several factors. First, the command elements are not only identifiable, but they make many synapses with other neurons, and the synapses are substantially invariant. There are separate flexion-producing and extension-producing command elements. Abdominal flexion-producing command elements excite other flexion elements and inhibit extensor command elements. The extension producing elements do the opposite. These interactions insure that interneurons of a particular class (flexion-or extension-producing) synaptically recruit perhaps twenty others of similar output, and that command elements promoting the opposing movements are inhibited. This strong reciprocity and the recruitment of similar command elements give a powerful motor program that appears to mimic behavior.
Extensor motor neurons of the crayfish abdomen
Journal of Comparative Physiology ? A, 1975
The somata of five deep extensor motoneurons of the third abdominal ganglion of the crayfish (Procambarus clarkii) were located and identified. The positions of these somata within the ganglion and their distal distribution to muscles have been mapped and were constant. The soma of the extensor inhibitor was noted to touch the soma of the flexor inhibitor. Three of the excitatory neurons were clustered near their exit route. Sensory and cord routes of activation of the extensor motoneurons were also found and were constant from preparation to preparation. Sub-threshold recording showed that these motoneurons exhibited radically different types of post-synaptie response to stimuli at different sites in the nervous system. No interaction between extensor motoneurons or between the extensor and flexor motoneurons was observed.
Adaptive motor control in crayfish
Progress in Neurobiology, 2001
This article reviews the principles that rule the organization of motor commands that have been described over the past ®ve decades in cray®sh. The adaptation of motor behaviors requires the integration of sensory cues into the motor command. The respective roles of central neural networks and sensory feedback are presented in the order of increasing complexity. The simplest circuits described are those involved in the control of a single joint during posture (negative feedback±resistance re¯ex) and movement (modulation of sensory feedback and reversal of the re¯ex into an assistance re¯ex). More complex integration is required to solve problems of coordination of joint movements in a pluri-segmental appendage, and coordination of dierent limbs and dierent motor systems. In addition, beyond the question of mechanical ®tting, the motor command must be appropriate to the behavioral context. Therefore, sensory information is used also to select adequate motor programs. A last aspect of adaptability concerns the possibility of neural networks to change their properties either temporarily (such on-line modulation exerted, for example, by presynaptic mechanisms) or more permanently (such as plastic changes that modify the synaptic ecacy). Finally, the question of how``automatic'' local component networks are controlled by descending pathways, in order to achieve behaviors, is discussed. 7
Abdominal positioning interneurons in crayfish: participation in behavioral acts
Journal of Comparative Physiology A, 1989
Intracellular recording, stimulation, and Lucifer dye injections were used to characterize abdominal positioning interneurons from the neuropile of the second through sixth abdominal ganglia of the crayfish, Procambarus clarhii. Motor outputs of these cells were recorded with extracellular electrodes placed on various flexion and extension roots along the nerve cord. In a n effort to assess the functional relationships between the postural interneurons in the abdomen and those known to exist in the circumesophageal connectives (CECs), a stimulus pulse train was delivered to each of the CECs while monitoring the intracellular responses of the impaled interneurons. Abdominal positioning interneurons were grouped into four general categories based on their responses to CEC stimulation: 1) those that projected their axons directly through the CECs; 2) those that were remotely activated to spiking; 3) those locally activated to produce EPSPs or IPSPs; and 4) those that were not affected by CEC stimulation.
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Computational neuroscience has a lot to gain from invertebrate research. In this chapter focusing on the sensory-motor network that controls leg movement and position in crayfish, we describe how simple neural circuitry can integrate variable information to produce an adapted output function. We describe how a specific sensor encodes the dynamic and static parameters of leg movements, and how the central motor network assimilates and reacts to this information. We then present an overview of the regulatory mechanisms thus far described that operate at the various levels of this sensory-motor network to organize and maintain the system into a dynamic range. On the basis of this simple animal model, some basic neurobiological concepts are presented which may provide new insights for engineering artificial autonomous systems.
Summary 1. An isolated preparation of the crayfish nervous system, comprising both the thoracic and the abdominal ganglia together with their nerve roots, has been used to study the influence of a single leg proprioceptor, the coxo-basal chordotonal organ (CBCO), on the fictive swimmeret beating consistently expressed in this preparation. Both mechanical stimulation of the CBCO and electrical stimulation of its nerve were used. 2. In preparations not displaying rhythmic activity, electrical or mechanical stimulations evoked excitatory postsynaptic potentials (EPSPs) in about 30 % of the studied motor neurones with a fairly short and regular delay, suggesting an oligosynaptic pathway. Such stimulation could evoke rhythmic activity in swim- meret motor nerves. The evoked swimmeret rhythm often continued for several seconds after the stimulus period. 3. When the swimmeret rhythm was well established, electrical and mechanical stimuli modified it in a number of ways. Limited mechanical ...